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Wp

PV system sizing

 

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1. Site survey (structures, electricalconsumers, meteorlogical data)

2. Determine consumer energy demand3. System voltage (12,24,48, 230V ?)4. Determine PV array power

 . eterm ne attery capac ty an vo tage6. Determine charge controller voltage and

current

7. Determine inverter power8. Determine cable size

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System voltage, depends on:

- Electrical devices (ac or dc)- Energy demand (approx. up to

1KVAh – 12V, up to 2,5KVAh –24V...)

- Cable lengths PV – battery andbattery – el. consumer

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Consumer energy demand:- Real power rating of ac devices (apparent

power)- Efficiency of inverter(app. 85-95%)

- .of rated power)

- Running time of devices (incl. Inverter)

= Battery discharge in Wh

divide by System Voltage

= Battery discharge in Ah

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Consumer Power demand:Device Wattage = inverter output power (VA)

cos phi

Inverter output = inverter input power (VA)Inv. eff.

-

Inverter

Output (VA)Input (VA)

Standby

 

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Consumer Energy demand:inverter input x hours = energy demand devices

inverter own consumption x hours = inverter energy demand

energy demand devices + inverter energy demand

=

consumer energy demand (VAh) = Battery discharge (Ah)Battery Voltage

Battery discharge (Ah) = Battery Capacity

DoD

Battery sizing:

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Batterydischarge

Batterychar e

C (Ah)

(Wh / Ah)

 

(Wh / Ah)

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Consumer

energyPV energydemand

Hours ?

Power ?

Cos Phi ?

Standby?

Eff.?

Out of MPP

operationlosses

25%

P  er f    or 

Charging

losses 5%

 

= BatteryDischarge

(Wh)

= BatteryCharge (Wh)

Electriclosses 5%

m an c e

     6     5     %

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100Wh65WhPV energy demand Consumer energy demand

Losses 35%

100Wh x 65% = 65Wh

65Wh / 65% = 100Wh

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Performance ratio (PR)

95%

 

65%

 en ca cu a ng• Current increases slightly

with temperature and at

operating point (app. 5%)• losses for dust• battery losses• charge controller losses

• wiring losses

en ca cu a ng• operating voltage (13,5V)

is app 25% less than Vmpp

• losses for dust• battery losses• charge controller losses• wiring losses

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PV energy demand , Battery charge

= Battery dischargePerformanceRatio

PV Power , PV Current

= PV energy demandPeak sun hours

Choose the right module and quantity

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Battery sizing:

consumer energy demand (VAh) = Battery discharge (Ah)Battery Voltage

Battery discharge (Ah) = Battery Capacity

o

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Battery capacity depends on:

• daily battery discharge (Ah) 

• Autonomy days

battery discharge x Autonomy daysDoDC =

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Charge controller size depends on:

• current from PV module(s) 

Add 20%

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Inverter size depends on:

• peak load of ac devices 

Add 100% for CFL due to harmonicsConsider starting current of motors

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cable size depends on:

• desired max voltage drop• length

• current

Allow max 3% voltage drop from PV tobattery and from battery to consumer